It was common up to now to make in thread-delivery devices the surface of the storage drum, which surface comes into contact with the thread windings, as smooth as possible, so that both the movement of the thread windings in the longitudinal direction of the drum and also the unwinding of the thread could take place under the least frictional influences. Thus for example the rods of rod drums, which rods are arranged approximately in the longitudinal direction around the drum axis, are made of steel, are ground and polished, or even chromium plated in order to achieve an as small as possible friction of the thread windings lying thereon. In the case of the usual threads this did lead to the desired result. However, in the case of so-called "sticky-yarns", namely in the case of threads which contain synthetic-fiber components or are synthetic and particularly are thin and elastic, and those threads which are waxed, oiled or impregnated, difficulties result during the movement of the thread windings which form the thread storage on the drum jacket, since these adhere and considerably resist the movement. During unwinding of the thread from the thread storage, same also adheres on the drum periphery, so that variations in the thread-withdrawing tension occur. These undesired effects can be found particularly with those adhering threads in a thread-storage and delivery device, as it is known from U.S. Pat. No. 3,904,141. This creates difficulties in evenly moving the thread windings forward. Furthermore those devices which are equipped with a storage drum which has longitudinal slots and webs operate with a feeler and spreading cone, which under a spring load opposite to the forward movement, rests on the front-most windings of the thread storage, measures the thread storage in this manner, and at the same time spreads open at least the front-most winding. During removal of the thread from the drum jacket, same adheres to the support surfaces of the webs, which results in a varying thread-withdrawing tension with tension peaks. The even advance of the thread windings and the constant and low withdrawing tension are, however, also conditions for a breakdown-free operation and qualitatively high-value woven or knitted products, in particular when using "sticky-yarns".
German AS No. 1 102 961 discloses a device for the delivery of thread to a circular knitting machine, in which a constantly rotated, cylindrical delivery drum has several individual side-by-side threads almost totally wound around it. When the knitting machine needs thread, it pulls on the thread, so that same more tightly loops around the drum jacket and, due to the then increasing friction, the thread is progressively delivered to the drum jacket. If the demand drops, the thread becomes loose, and the drum rotates within the thread loop. The drum is here coated with a silicon rubber, which has a smooth surface with a certain friction value with respect to the thread. In order to be able to deliver the threads which lie side-by-side in the longitudinal direction of the drum with speeds which are different from one another, it is furthermore suggested to provide side-by-side lying ring zones on the drum which have surface characteristics and sliding resistances which are different from one another. The ring zone with the largest friction factor results, at a constant thread-looping force and drum speed, in the largest thread-delivery output. All these measures are, however, not advantageous for storage devices of the type mentioned in the beginning, since also in the case of the lastmentioned delivery drum the thread windings, in particular of sticky-yarns, due to the existing adhesion tendency, grip on smooth surfaces relatively independently of the sliding resistance but in dependency on the size of the contact surface.
The basic purpose of the invention is to improve a device of the abovementioned type so that also in the case of "sticky-yarns" the thread advance takes place easily and evenly and the thread-withdrawing tension remains low and even. This purpose is attained inventively by the provision, on the drum, of roughened or interrupted contact surfaces for the thread windings. Surprisingly such a roughened or interrupted contact surface for the thread windings of a "sticky-yarn" shows that the advancing movement now faces a substantially lower resistance and that the thread-withdrawing tension variations are totally eliminated. Even though one actually expected that those thread types which are difficult to handle would be still more difficult to move on a rough contact surface and would even get hooked during the withdrawal, exactly the opposite effect is observed. The achieved advantages can probably be explained by the "sticky-yarns" having a tendency for adhesion which is caused by the material or by impregnation or composition. This effect is similar to the adhesive effect which occurs during the relative movement or separation of two, possibly slimy, glass plates and which is caused by the air pressure or a pressure difference, or the adhesion of a smooth sheet of paper on a sweaty hand, Also the electrostatic charge of the thread can here contribute to the increase in the tendency to adhere. If now the thread finds a connected, larger and smooth contact surface on the drum jacket, a plurality of adhesive force components is formed, which sum up to a resulting force up to the moment of movement or releasing, which force makes movement in the longitudinal direction of the drum and also the withdrawal of the thread more difficult. The plurality of interruptions or recesses according to this invention causes the thread windings to contact only the raised, substantially reduced surface sections, on which an adhesion can hardly occur. Since the surface sections, however, amount only to a fraction of the actually existing drum surface, the entire adhesive force becomes substantially lower than is the case with a continuous and smooth surface. The thread windings do not find a connected contact surface, but so to speak many small surface units. Instead of an adhesion which occurs along one line only, dotlike adhesive areas with very small adhesive forces exist. These then do not sum up in one point, but are overcome at the various points of creation. Since in the peripheral direction of the storage drum a relative movement between the thread windings and the drum does not occur, the replacement of a smooth surface with a surface which is interrupted in the peripheral direction does not have any effect at all. The raised surface sections can even form a structuring which approximately equals the skin of an orange. The thread can easily slide thereon without getting hooked.
The Swedish patent application No. 345 293 as published May 23, 1972, does disclose providing an intermittent feed of threads with different adhesive tendency to a knitting machine, each thread of which is looped around a friction roller at least one time for 360.degree.. Depending on the adhesive tendency of the thread, a friction roller which differs in diameter and/or surface structure is utilized. For particularly adhesive-happy threads, the surface is roughed up by sand blasting in order to produce a larger friction coefficient for the thread. In this manner the slip can be adjusted so that, in a peripheral direction, the actually different threads are delivered with the same speed or thread tension. The principle is hereby to provide a thread which actually slides easily with an adhesive tendency caused by its material structure, and a rough rotating roller surface with which both its sliding friendliness is suppressed through an increased friction and also its inherent adhesive tendency is overcome by the increased friction. The condition is thereby, however, that in the peripheral direction of the friction roller there exists a relative movement between the thread and the roller. This principle is therefore without importance for a device of the abovementioned type, in which relative movements in the peripheral direction do not take place between the thread windings and the drum jacket. Rather, a roughing up of the drum jacket through sand blasting would produce pointed surface peaks, which cause a hooking of the thread windings and make the advancing movement, occurring in the longitudinal direction of the drum, impossible.
In a preferred embodiment of this invention, the drum has elevated surface sections which extend in the axial direction. Here too it is observed that the movement of the thread windings and the withdrawal takes place surprisingly easily.
A further advantageous exemplary embodiment of this invention, as applied to a storage drum of rods which are arranged cagelike around the drum axis and are approximately parallel to one another, provides the rods with surface profiles, like serrations, which extend longitudinally of the rods. A substantially reduced contact surface is offered aligned in the longitudinal direction of the drum to the on-lying thread windings, so that the adhesive tendency of the thread can now lead to insignificant resistive forces in relationship to the advancing movement and the withdrawal of the thread.
The material selection in connection with the reduced contact surface reduces the adhesion of the thread windings still further. Furhermore in the case of rods which are extruded from aluminum the longitudinal grooves can be formed very well. The rods can be manufactured inexpensively and with constant dimensions.
Further, advantageous embodiments of the subject matter of the application are disclosed in the following, including in particular a method for causing a hard-eloxation which has extremely desired roughness or gripping capacity, and which in addition is very durable.
Embodiments of the subject matter of the invention will be discussed in more detail hereinafter.